A head-mounted display (HMD) is a portable display device worn on a head, and is an apparatus having a display device that is mounted on a head in the form of, for example, goggles or a helmet to define a focal point of an image at a very short distance in front of eyes. A user wearing a HMD feels in a virtual reality because the entire field of view is covered by an image, and thus a HMD has applications in various fields for military, medical and personal uses.
For example, Japanese Patent Application Publication No. 1999-161190 discloses detecting a motion of a head part of a user, and controlling information displayed on a display device through the detected results. However, a disadvantage of this conventional HMD is that the user's motion is only used to change the viewpoint displayed on the display device, and in order to perform control such as event processing of the displayed information, a separate controller, for example, a touch pad and a game pad is needed.